It is desirable for a broad range of water insoluble materials, including hydrocarbons, higher alkyl esters, natural and synthetic waxes, resins, and water in oil emulsions, particularly those associated with coatings and color cosmetics to contain dispersible particles in order to vary film strength, barrier properties, color and emollient character. The dispersion of pigments can be controlled by a number of methods including introducing surface charge (controlling zeta potential) and modifying hydrophobicity or hydrophilicity. In most of these approaches the pigment's surface is considered to present a homogeneous surface that dictates the dispersibility of the particle. A simple example is the inability to disperse pyrogenic silica as a stable suspension in water after it has been made hydrophobic by treatment with hexamethyldisilazane despite the fact that it is denser than water. In the absence of treatment, pyrogenic silica sinks in water and forms agglomerates. On the other hand, the hexamethyldisilazane silica disperses well in hydrophobic media such as silicone and mineral oils.
The use of organosilane treatments to improve the wetting and dispersion of pigments and fillers in a variety of vehicles is well known. U.S. Pat. No. 4,169,912 teaches alkyl, alkenyl, or aryl silane surface treatment of iron oxides to improve dispersibility in organic media. U.S. Pat. No. 4,344,799 discloses the use of alkyl silane treatment to produce a titanium dioxide pigment that is readily dispersible in lacquers and plastics. U.S. Pat. No. 4,421,747 discloses high solids coatings having reduced viscosities, achieved by pre-treating pigments with alkyl silanes and titanates. U.S. Pat. No. 4,578,266 teaches that use of polysiloxane coatings on pigment formed by treatment with reactive silicones or silanes permits the incorporation of unexpectedly high amounts of pigment in silicone-containing systems.
Silanes containing relatively hydrophilic polyethylene glycol (PEG) substituent groups also have been used to modify dispersion properties. U.S. Pat. Nos. 4,061,503 and 4,151,154 disclose the use of silanes containing at least one alkylene group to improve dispersion of pigments and fillers in resin or plastic. However, there remains a need in the art for materials that may further improve the wettability and/or dispersibility of inorganic materials, such as pigments.